Recent evidence suggests that reperfusion injury following myocardial ischemia is mediated by an excess of oxygen free radicals. The glutathione redox cycle has been shown to be important in preventing myocardial reperfusion injury has not been fully evaluated. In this proposal it is planned to use a unique application of proton magnetic resonance spectroscopy (1H-MRS) to examine the role of the glutathione redox cycle in modulating reperfusion injury. Three hypotheses are to be tested: 1) proton magnet resonance (1H-MRS) can be applied to determine nondestructively the state of the glutathione redox cycle both in vitro and in vivo, 2) the myocardial response to hypoxia/reoxygenation and ischemia/reperfusion depends upon a normally functioning glutathione redox cycle, and 3) enhancing glutathione oxidation will decrease myocardial reperfusion injury. Thus 1H-MRS techniques will be developed and verified for the measurement of reduced glutathione (GSH) and oxidized glutathione (GSSG), and for the continuous measurement of GSH as it is oxidized. To test the second hypothesis the myocardial functional, biochemical, and structural response will be tested during manipulation of the glutathione redox cycle in 1) the isolated perfused rat heart during ischemia/reperfusion, hypoxia/reoxygenation, or activated leukocyte infusion, and in 2) an open chest rat model during and following temporary coronary artery ligation. The cycle will be manipulated using buthionine sulfoximine, diethylmalate, 1, 3-bis (2-chloroethyl)-1 nitrosurea, or chronic selenium deficiency. The myocardial response will be determined by measuring high energy phosphates with phosphorus magnetic resonance spectroscopy, creatine kinase release, cardiac malondialdehyde, ventricular function, myocardial lactate during ischemia by 1H-MRS, and cardiac histology, including infarct size determination in the in vivo model. Finally, the third hypothesis will be tested by comparing the myocardial response to ischemia and reperfusion both in vivo and in vitro when extracellular glutathione oxidation is enhanced with GSH, or when intracellular glutathione oxidation is enhanced by GSH monoethyl ester. It is anticipated that these studies will delineate the role of the gluathione redox cycle in ameliorating reperfusion injury and form a basis for future clinical studies.